Annex C (informative) Compatibility [diff]

C.1 C++ and ISO C++ 2020 [diff.cpp20]

C.1.9 [mem]: memory management library [diff.cpp20.memory]

Affected subclause: [allocator.traits.general]
Change: Forbid partial and explicit program-defined specializations of allocator_traits.

Rationale: Allow addition of allocate_at_least to allocator_traits, and potentially other members in the future.

Effect on original feature: Valid C++ 2020 code that partially or explicitly specializes allocator_traits is ill-formed with no diagnostic required in this revision of C++.